1. Field of the Invention
The present invention relates to an inter-line type charge coupled device (CCD) solid state image pickup apparatus (CCD apparatus).
2. Description of the Related Art
Two-dimensional CCD solid state pickup apparatuses instead of pickup tubes have been used in family video cameras, electronic news gathering (ENG) cameras and the like.
Generally, a CCD apparatus includes two-dimensionally arranged photodiodes in rows, columns; a plurality of vertical transfer registers, each connected to one column of the photodiodes; and a horizontal transfer register connected to the vertical transfer registers. In the CCD apparatus, signal charges are transferred from the photodiodes to the vertical transfer registers; however, smear charges are also transferred to the vertical transfer registers. Such smear charges cause image defects which appear to be extended within the vertical transfer registers. Particularly, CCD apparatuses have recently been fine-structured to obtain a high resolution; however, in this case, the characteristics of the CCD apparatus such as the smear characteristics and the dynamic range have been deteriorated. That is, in the CCD apparatus, the high resolution has a trade-off relationship with the characteristics. This will be explained later in detail.
In order to improve the smear characteristics and increase the dynamic range, in a prior art inter-line type CCD apparatus (see JP-A-4-330876), a horizontal transfer register for transferring smear charges is added to a horizontal transfer register for transferring signal charges including smear charges. In a low luminescence state, an output voltage is obtained by subtracting a voltage corresponding to the smear charges from a voltage corresponding to the signal charges including smear charges. Thus, the component of smear charges is suppressed in the output voltage, to improve the smear characteristics. On the other hand, in a high luminescence state, the output voltage can be increased by adding the voltage corresponding to smear charges thereto, thus increasing the dynamic range. In this prior art CCD apparatus, however, the resolution in a high luminescence state is still deteriorated. This will also be explained later in detail.